Monochromatic Light Driven Synthesis and Growth of Flat Silver Nanoparticles and their Plasmon Sensitivity

Size and shape of metal nanoparticles play a key role in most of their technological applications because they determine their optical properties in the UV-vis-NIR range as well as their interaction with molecules at the surroundings. In this paper we demonstrate the “in liquid” formation of flat silver nanoparticles’ colloids through a wise use of pulsed laser beams and monochromatic LEDs. A spherical to flat nanoparticles transformation is driven and sustained by the addition of H2O2 and citrate during the light irradiation. In this respect it is demonstrated that high citrate concentrations limit the growth of some crystalline facets, confining the plasmon resonance of the final colloid to the visible region, while the use of lower concentrations results in the formation of large plates with resonances in the near infrared. Thus the manipulation of citrate concentration in the solution and the choice of the irradiation wavelength give the possibility to tune the position of the main plasmon resonance across the visible and near IR part of the spectrum. Plasmon sensitivity measurements show that nanoplates irradiated at the longest wavelenghts have the highest response to refractive index change.